Inkjet technology is now used in a wide variety of applications. Originally, inkjet techniques were developed in printers that selectively eject drops of ink or other marking fluid onto a printing medium to produce a hardcopy document from electronic data. More recently, inkjet techniques have been used in such diverse applications as fuel injectors and three-dimensional freeform fabrication systems.
As used herein and in the appended claims, the term “printing device” will be used to refer to any device for whatever application that ejects a fluid using inkjet printing techniques, including, thermal and piezo-electric inkjet printing techniques.
At the manufacturing level, inkjet printing devices for virtually any application are subjected to various tests before being released for sale to the consumer. These tests determine whether the inkjet nozzles are functional and whether the print head is properly aligned with respect to other print heads used in the system.
Further, consumers must maintain their printers by periodically performing maintenance tests to ensure that the print nozzles are functional, and that the print head is properly aligned. These tests are similar or identical to tests performed by the manufacturer.
A particular problem associated with such tests is the need to test not only the flow of colored fluids, but also the flow of clear fluids such as binders, build materials, fuels, etc. It is difficult or impossible to see such clear fluids on paper. Consequently, it is not very effective to test the print head by attempting to deposit fluid on a sheet of paper. However, this is the conventional method of testing the operation of an inkjet print head.
In some alignment tests, where the print head uses a clear fluid, black ink is used so that operation of the print head can be observed. Then the black ink is purged from the print head and the print head is supplied with the desired clear fluid. However, if the print head has to be removed and reinstalled after purging the black ink, there is no method for realigning the print head that is now using a clear fluid.
Currently there are several methods that are used to visualize clear or light colored fluids after ejection so that the correct operation of the print head can be observed and verified. One very popular method involves the addition of an ultraviolet (UV) indicator to the ink or fluid being ejected. After the test cycle is finished, the clear or light colored fluid can be viewed when UV light is emitted onto the pattern of ejected fluid. However, the UV indicator is an expensive additive. Moreover, it is not practical or cost effective for every printer technician or owner to purchase a UV light and to be subject to the complexity of adding UV indicator to the print fluid or to purchase print fluid that includes UV indicator. Some printers are equipped with a UV light emitter, but this adds to the expense of the printer.
Another method that is currently used for visualizing clear or light colored fluid involves viewing clear fixer on a transparent or glossy medium. This method is also commonly used for viewing clear binder. Such a method is used somewhat successfully in printer alignment tests, but is not considered adequate for nozzle health tests. In either case, it is still difficult to visualize transparent or light colored fluids on a clear or glossy background.